The present invention relates to a head gimbal assembly used in disk drives. More particularly, this invention pertains to a head gimbal assembly having features for improved ESD protection.
Disk drives are commonly employed in workstations, personal computers, portables and other computer systems to store large amounts of data in a readily-available form. Typically, the primary components of a disk drive are a head disk assembly and a printed circuit board assembly which when fixed to one another form a functional unit that is then connected to a computer, such as by insertion into a bay of a host computer.
The head disk assembly includes a base and a cover which collectively house an actuator arrangement, driven by a voice coil motor and comprising a head stack assembly, and at least one data storage disk mounted on a spindle motor for rotating the storage disk. The head stack assembly comprises one or more head gimbal assemblies, each comprising a head or xe2x80x9csliderxe2x80x9d connected to a trace gimbal assembly having pairs of read and write traces for connecting the head to the printed circuit board assembly. The trace gimbal assembly is typically mounted to a conductive substrate such as a load beam for supporting the read and write traces and the head.
In current disk drives, head read elements are formed with Giant Magnetoresistive (GMR) elements which are being continually driven to smaller geometries to be compatible with increasing track densities required to meet capacity targets. Unfortunately, the diminishing size of the heads have made them increasingly vulnerable to electrostatic discharges (ESD) during the various stages of the manufacturing process, particularly during the pre-head disk assembly stages. Because of the small physical size of today""s heads, very low discharge levels can be more than sufficient to destroy the head.
The head is also susceptible to damages caused by electrical overstress (EOS) events which typically occur at even lower potential differences than those causing an ESD event. Additionally, damages caused by ESD and EOS events can be hard to detect prior to the final assembly and testing of the disk drive, at which time replacing and repairing of the damaged head proves to be the most expensive and can cause reliability problems due to an overstressed head. It is therefore highly desirable to prevent ESD and EOS events from occurring during all stages of the manufacturing of the head stack assembly.
Currently, one form of reducing the occurrence of ESD and EOS events is by use of a shunt to short circuit the read element in the head. The shunt approach is not without shortcomings. One shortcoming of the shunt is that although the shunt protects the head against the occurrence of ESD and EOS events, it also virtually precludes testing the shunted element. To address this problem, a switched shunt has been used which can be set to an open position while testing of the read element and then closed to a short-circuit position at other times. In common practice, a switched shunt is placed at a distal end of the trace gimbal assembly so that it can be removed prior to the final integration of the head gimbal assembly into the head stack assembly. This distancing, however, diminishes the effectiveness of the shunt in protecting the head.
Another currently utilized form of reducing the occurrence of ESD and EOS events is by use of an anti-static coating applied on the head gimbal assembly. The anti-static coating functions to dissipate the accumulated charge thereby reducing the occurrence of ESD and EOS events. The use of anti-static coating, however, is not without shortcomings. The anti-static coating cannot be applied to all regions of the trace gimbal assembly due to non-ESD and EOS related mechanical and chemical considerations. For example, if too thick an anti-static coating is applied it may cause adverse stiffness in the gimbal area. If too little anti-static coating is applied, it may not sufficiently adhere to head gimbal assembly and become detached during the operation of the disk drive.
Accordingly, what is needed is a head gimbal assembly that has reduced susceptibility to ESD and EOS events.
This invention can be regarded as a Trace Gimbal Assembly (TGA) for use in a disk drive, wherein the TGA is attachable to a head having a read element and a write element. The TGA includes a conductor array having a first end connectable to the read element and the write element and a distal end for connecting the read element and the write element to a signal processing circuit. A conductive substrate supports the head and the conductor array. A dielectric layer is disposed between the conductor array and the conductive substrate. The TGA further includes a shunt connected at the distal end for shunting the read element; and an anti-static coating, covering a substantial portion of the conductor array for neutralizing electrostatic charge accumulation on the conductor array.
This invention can also be regarded as a Head Gimbal Assembly (HGA) for use in a disk drive. The HGA includes a head having a read element and a write element; and a Trace Gimbal Assembly (TGA) attached to the head. The TGA includes a conductor array having a first end connected to the read element and the write element and a distal end for connecting the read element and the write element to a signal processing circuit, a conductive substrate supporting the head and the conductor array and a dielectric layer disposed between the conductor array and the conductive substrate. The TGA further includes a shunt connected at the distal end for shunting the read element; and an anti-static coating, covering a substantial portion of the conductor array for neutralizing electrostatic charge accumulation on the conductor array.